The present invention is directed to the separation of polynucleotides using a separation medium having non-polar surfaces, such as the surfaces of nonporous beads or surfaces of interstitial spaces within a molded monolith (e.g., a derivatized silica monolith), which surfaces are substantially free from contamination with multivalent cations. More specifically, the invention is directed to the chromatographic separation of both single stranded and double stranded polynucleotides by chromatography using a nonporous separation medium, where the medium is either organic or inorganic material which is coated with a polymer, or non-polar substituted polymer, and/or which has substantially all surface substrate groups substituted with a non-polar hydrocarbon or non-ionic substituted hydrocarbon.
Separations of polynucleotides such as DNA have been traditionally performed using slab gel electrophoresis or capillary electrophoresis. However, liquid chromatographic separations of polynucleotides are becoming more important because of the ability to automate the analysis and to collect fractions after they have been separated. Therefore, columns for polynucleotide separation by liquid chromatography (LC) are becoming more important.
Silica-based columns are by far the most common LC columns. Of these, reverse phase silica-based columns are preferred because they have high separation efficiencies, are mechanically stable, and a variety of functional groups can be easily attached for a variety of column selectivities.
Although silica-based reverse phase column materials have performed adequately for separating single stranded DNA, these materials have not performed well for separating double stranded DNA. The peaks from double stranded DNA separations using silica-based materials are badly shaped or broad, or the double stranded DNA may not even elute. Separations can take up to several hours, or the resolution, peak symmetry, and sensitivity of the separation are poor.
High quality materials for DNA separations have been based on polymeric substrates, as disclosed in U.S. Pat. No. 5,585,236 to Bonn (1966). There exists a need for silica-based column packing material and other materials that are suitable for separation of double stranded DNA.
Accordingly, one object of the present invention is to provide a chromatographic method for separating polynucleotides with improved separation and efficiency. Another object is to provide improved non-polar separation media for the separation of polynucleotides.
These and other objects of the invention, which will become apparent from reading the following specification, have been achieved by the method of the present invention in which polynucleotides are separated using a nonporous separation medium such as beads or a molded monolith (e.g., a silica gel monolith), where the medium comprises either organic or inorganic material which is coated with a polymer, or non-polar substituted polymer, and/or which has substantially all surface substrate groups substituted with a non-polar hydrocarbon or non-ionic substituted hydrocarbon.
In one aspect, the invention is a method for separating a mixture of polynucleotides comprising applying a mixture of polynucleotides having up to 1500 base pairs to a separation medium, the separation surfaces of the medium coated with a hydrocarbon or non-polar hydrocarbon substituted polymer, or having substantially all polar groups reacted with a non-polar hydrocarbon or substituted hydrocarbon group, wherein said surfaces are non-polar; and eluting the polynucleotides. The separation medium can be enclosed in a column. Examples of non-polar surfaces include the surfaces of beads such as nonporous particles and the surfaces of intersitital spaces within a monolith (e.g., a silica gel monolith), which surfaces are coated with a hydrocarbon or non-polar substituted polymer or having substantially all surface substrate groups reacted with a non-polar hydrocarbon or substituted hydrocarbon group. In the preferred embodiment, precautions are taken during the production of the medium so that it is substantially free of multivalent cation contaminants and the medium is treated, for example by an acid wash treatment and/or treatment with multivalent cation binding agent, to substantially remove any residual surface metal contaminants. The preferred separation medium is characterized by having a DNA Separation Factor (defined hereinbelow) of at least 0.05. The preferred medium is characterized by having a Mutation Separation Factor (as defined hereinbelow) of at least 0.1. In a preferred embodiment, the separation is made by Matched Ion Polynucleotide Chromatography (MIPC, as defined hereinbelow). The elution step preferably uses a mobile phase containing a counterion agent and a water-soluble organic solvent. Examples of a suitable organic solvent include alcohol, nitrile, dimethylformamide, tetrahydrofuran, ester, ether, and mixtures of one or more thereof, e.g., methanol, ethanol, 2-propanol, 1-propanol, tetrahydrofuran, ethyl acetate, acetonitrile. The most preferred organic solvent is acetonitrile. The counterion agent is preferably selected from the group consisting of lower primary amine, lower secondary amine, lower tertiary amine, lower trialkyammonium salt, quaternary ammonium salt, and mixtures of one or more thereof. Non-limiting examples of counterion agents include octylammonium acetate, octyldimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, or bromide. The most preferred counterion agent is triethylammonium acetate or triethylammonium hexafluoroisopropyl alcohol.
One embodiment of the invention provides a method for separating a mixture of polynucleotides, comprising applying a mixture of polynucleotides having up to 1500 base pairs to separation beads having non-polar surfaces, and eluting said mixture of polynucleotides. In a particular embodiment of the separation medium, the invention provides a method for separating a mixture of polynucleotides comprising applying a mixture of polynucleotides having up to 1500 base pairs through a separation column containing beads which are substantially free from contamination with multivalent cations and having an average diameter of 0.5 to 100 microns, and eluting the mixture of polynucleotides. In one embodiment, the beads comprise nonporous particles coated with a hydrocarbon or non-polar substituted polymer or having substantially all surface substrate groups reacted with a non-polar hydrocarbon or substituted hydrocarbon group. The beads preferably have an average diameter of about 1-5 microns. In the preferred embodiment, precautions are taken during the production of the beads so that they are substantially free of multivalent cation contaminants and the beads are treated, for example, by an acid wash treatment and/or treatment with multivalent cation binding agent, to remove any residual surface metal contaminants. The beads of the invention are characterized by having a DNA Separation Factor of at least 0.05. In a preferred embodiment, the beads are characterized by having a DNA Separation Factor of at least 0.5. Also in a preferred embodiment, the beads are characterized by having a Mutation Separation Factor of at least 0.1. In one embodiment, the beads are used in a capillary column to separate a mixture of polynucleotides by capillary electrochromatography. In other embodiments, the beads are used to separate the mixture by thin-layer chromatography or by high-speed thin-layer chromatography. The separation is preferably by MIPC. The beads preferably have an average diameter of about 1-5 microns. The nonporous particle is preferably selected from silica, silica carbide, silica nitrite, titanium oxide, aluminum oxide, zirconium oxide, carbon, insoluble polysaccharides such as cellulose, and diatomaceous earth, or any of these materials that have been modified to be nonporous. The nonporous particle is most preferably silica, which preferably is substantially free from underivatized silanol groups. The particles can be prepared by non-covalently bonded coatings, covalently bonded coatings, or reaction of the silanol groups with hydrocarbon groups.
The nonporous particle can be coated with a polymer. The polymer is preferably selected from polystyrenes, polymethacrylates, polyethylenes, polyurethanes, polypropylenes, polyamides, cellulose, polydimethyl siloxane, and polydialkyl siloxane. The polymer is optionally unsubstituted or substituted with hydrocarbon groups or other groups having nonionic substituents. The polymer can be optionally substituted with hydrocarbon groups having from 1 to 1,000,000 carbons, the hydrocarbon groups optionally being alkyl groups with from 1 to 100 carbons and preferably from 1 to 24 carbons. Hydrocarbon groups from 24 to 1,000,000 are described herein as hydrocarbon polymers and have the constituency of hydrocarbon groups as defined herein.
The reaction of organosilanols (e.g. HOxe2x80x94Sixe2x80x94R3) or alkoxy- (e.g., ROxe2x80x94Sixe2x80x94R3) silanes with silica supports without polymerization can also produce good packings. The method produces a dense monolayer of functional groups of alkyl or alkylsubstituted, ester, cyano, and other nonionic groups. The use of monofunctional dimethyl silanes (Xxe2x80x94Si(CH3)2xe2x80x94R) provides a homogeneous organic coating with a minimum of residual Sixe2x80x94OH groups. Monochlorosilane reagents are preferred, if the required organic functionality can be prepared. These reactions are reproducible and provide high quality packing materials. Unreacted, accessible silanols can be left after the initial reaction. The nonporous particle is preferably endcapped with a tri(lower alkyl)chlorosilane (preferably a trimethylchlorosilane) to block residual reactive silanol sites following the coating or hydrocarbon substitution. Alternatively, all of the silanol sites can be reacted with an excess of the endcapping reagent to extinguish all reactive silanol groups. Endcapping of the nonporous particle can be effected by reaction of the nonporous particle with the corresponding hydrocarbon substituted halosilane, such as trialkyl chlorosilane (eg. trimethyl chlorosilane) or by reaction with the corresponding hydrocarbon substituted disilazane, such as dichloro-tetraalkyl-disilazane (eg. dichloro-tetramethyl-disilazane).
The method of the present invention can be used to separate double stranded polynucleotides having up to about 1500 to 2000 base pairs. In many cases, the method is used to separate polynucleotides having up to 600 bases or base pairs, or which have up to 5 to 80 bases or base pairs.
The method is performed at a temperature within the range of 20xc2x0 C. to 90xc2x0 C. The flow-rate of the mobile phase is preferably adjusted to yield a back-pressure not greater than 10,000 psi. The method also preferably employs an organic solvent and more preferably an organic solvent that is water soluble. The solvent is preferably selected from the group consisting of alcohols, nitriles, dimethylformamide, esters, and ethers. The method also preferably employs a counterion agent selected from trialkylamine acetate, trialkylamine carbonate, and trialkylamine phosphate. The most preferred counterion agent is triethylammonium acetate or triethylammonium hexafluoroisopropyl alcohol.
In addition to the beads or other medium being substantially metal-free, Applicants have also found, that to achieve optimum peak separation, the inner surfaces of the column (or other container) and all process solutions held within the separation system or flowing through the system are preferably substantially free of multivalent cation contaminants. The method preferably comprises supplying and feeding solutions entering the separation column with components having process solution-contacting surfaces which contact process solutions held therein or flowing therethrough. The process solution-contacting surfaces are material which does not release multivalent cations into aqueous solutions held therein or flowing therethrough, so that the column and its contents are protected from multivalent cation contamination The process solution-contacting surfaces are preferably material selected from the group consisting of titanium, coated stainless steel, passivated stainless steel, and organic polymer. Multivalent cations in mobile phase solutions and sample solutions entering the column are also preferably removed by contacting the solutions with multivalent cation capture resin before the solutions enter the column so as to protect the separation medium from multivalent cation contamination. The multivalent capture resin is selected from cation exchange resin and chelating resin. The column and process solutions held therein or flowing therethrough are preferably substantially free of multivalent cation contaminants. The polynucleotides are separated by Matched Ion Polynucleotide Chromatography.
Also disclosed herein is a method for separating a mixture of polynucleotides, comprising flowing a mixture of polynucleotides having up to 1500 base pairs through a separation column containing beads having an average diameter of 0.5 to 100 microns, and separating the mixture of polynucleotides by Matched Ion Polynucleotide Chromatography. The beads comprise nonporous particles coated with a polymer or having substantially all surface substrate groups reacted and/or endcapped with a non-polar hydrocarbon or substituted hydrocarbon group. The beads are characterized by having a DNA Separation Factor of at least 0.05.
Also disclosed herein is a bead comprising a nonporous particle coated with a polymer. The bead has an average diameter of 0.5 to 100 microns and is characterized by having a DNA Separation Factor of at least 0.05. In a preferred embodiment, the bead is characterized by having a DNA Separation Factor of at least 0.5. The preferred bead is characterized by having a Mutation Separation Factor of at least 0.1. The bead preferably has a diameter of about 1-5 microns. The nonporous particle is preferably selected from silica, silica carbide, silica nitrite, titanium oxide, aluminum oxide, zirconium oxide, carbon, insoluble polysaccharides such as cellulose, and diatomaceous earth, or any of these materials that have been modified to be nonporous. The nonporous particle is most preferably silica, which preferably has minimum silanol groups. The polymer is preferably selected from polystyrene, polymethacrylate, polyethylene, polyurethane, polypropylene, polyamide, cellulose, polydimethyl siloxane, and polydialkyl siloxane, and is preferably unsubstituted, alkylated, or alkyl or aryl substituted, or alkylated with a substituted alkyl group methyl-substituted, or ethyl-substituded. The polymer can be alkylated with alkyl groups having 1-22 carbon atoms, preferably, 8-18 carbon atoms.
Also disclosed herein is a bead comprising a nonporous particle having substantially all surface substrate groups reacted with a hydrocarbon group and then endcapped with a non-polar hydrocarbon or substituted hydrocarbon group, preferably a tri(lower alkyl)chlorosilane or tetra(lower alkyl)dichlorodisilazane. The bead has an average diameter of 0.5 to 100 microns and is characterized by having a DNA Separation Factor of at least 0.05. The bead preferably has a diameter of about 1-5 microns.
The nonporous particle is preferably selected from silica, silica carbide, silica nitrite, titanium oxide, aluminum oxide, zirconium oxide, carbon, insoluble polysaccharides such as cellulose, and diatomaceous earth, or any of these materials that have been modified to be nonporous. The nonporous particle is most preferably silica, which preferably has minimum silanol groups. Endcapping of the nonporous particle can be effected by reaction of the nonporous particle with trimethyl chlorosilane or dichloro-tetraisopropyl-disilazane.
In a still further aspect, the invention is a method for separating a mixture of polynucleotides comprising applying a mixture of polynucleotides having up to 1500 base pairs to a monolith having non-polar separation surfaces, and eluting the polynucleotides. The monolith can be enclosed in a column or other containment system, such as a cartridge. In a preferred embodiment, the monolith is a silica gel monolith. The non-polar separation surfaces include the surfaces of intersitital spaces within the monolith, which surfaces are coated with a hydrocarbon or non-polar substituted polymer or having substantially all surface substrate groups reacted with a non-polar hydrocarbon or substituted hydrocarbon group. An example of a suitable monolith is one which is polyfunctionally derivatized with octadecylsilyl groups. In the preferred embodiment, precautions are taken during the production of the monolith so that it is substantially free of multivalent cation contaminants and the monolith is treated, for example by an acid wash treatment and/or treatment with multivalent cation binding agent, to substantially remove any residual surface metal contaminants. The preferred monolith is characterized by having a DNA Separation Factor of at least 0.05. The preferred monolith is characterized by having a Mutation Separation Factor of at least 0.1. In a preferred embodiment, the separation is made by Matched Ion Polynucleotide Chromatography. The elution step preferably uses a mobile phase containing a counterion agent and a water-soluble organic solvent. Examples of a suitable organic solvent include alcohol, nitrile, dimethylformamide, tetrahydrofuran, ester, ether, and mixtures of one or more thereof, e.g., methanol, ethanol, 2-propanol, 1-propanol, tetrahydrofuran, ethyl acetate, acetonitrile. The most preferred organic solvent is acetonitrile. The counterion agent is preferably selected from the group consisting of lower primary amine, lower secondary amine, lower tertiary amine, lower trialkyammonium salt, quaternary ammonium salt, and mixtures of one or more thereof. Non-limiting examples of counterion agents include octylammonium acetate, octyldimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, or bromide. The most preferred counterion agent is triethylammonium acetate or triethylammonium hexafluoroisopropyl alcohol.
In a yet further aspect, the invention provides a monolith having non-polar separation surfaces which are substantially free from contamination with multivalent cations. The monolith can be enclosed in a column or other containment system, such as a cartridge. The non-polar separation surfaces include the surfaces of interstitial spaces within the monolith (e.g., a silica monolith), which surfaces are coated with a hydrocarbon or non-polar substituted polymer or having substantially all surface substrate groups reacted with a non-polar hydrocarbon or substituted hydrocarbon group. An example of a suitable monolith is one which is derivatized with polyfunctionally derivatized octadecylsilyl groups. In the preferred embodiment, precautions are taken during the production of the monolith so that it is substantially free of multivalent cation contaminants and the monolith is treated, for example by an acid wash treatment and/or treatment with multivalent cation binding agent, to remove any residual surface metal contaminants. The preferred monolith is characterized by having a DNA Separation Factor of at least 0.05. The preferred monolith is characterized by having a Mutation Separation Factor of at least 0.1.
In addition to the beads (or other media) themselves being substantially metal-free, Applicants have also found that to achieve optimum peak separation the inner surfaces of the separation column (or other container) and all process solutions held within the column or flowing through the column are preferably substantially free of multivalent cation contaminants. This can be achieved by supplying and feeding solutions entering the separation column with components which have process solution-contacting surfaces made of material which does not release multivalent cations into the process solutions held within or flowing through the column, in order to protect the column from multivalent cation contamination. The process solution-contacting surfaces of the system components are preferably material selected from the group consisting of titanium, coated stainless steel, and organic polymer. For additional protection, multivalent cations in mobile phase solutions and sample solutions entering the column can be removed by contacting these solutions with multivalent cation capture resin before the solutions enter the column to protect the separation medium from multivalent cation contamination. The multivalent capture resin is preferably cation exchange resin and/or chelating resin.
In another aspect, the present invention is a method for treating the non-polar surfaces of a medium used for separating polynucleotides, such as the surfaces of beads in a MIPC column or the surfaces of interstitial spaces in a monolith, in order to improve the resolution of polynucleotides, such as dsDNA, separated on said surfaces. This treatment includes contacting the surface with a solution containing a multivalent cation binding agent. In a preferred embodiment, the solution has a temperature of about 50xc2x0 C. to 90xc2x0 C. An example of this treatment includes flowing a solution containing a multivalent cation binding agent through a MIPC column, wherein the solution has a temperature of about 50xc2x0 C. to 90xc2x0 C. The preferred temperature is about 70xc2x0 C. to 80xc2x0 C. In a preferred embodiment, the multivalent cation binding agent is a coordination compound, examples of which include water-soluble chelating agents and crown ethers. Specific examples include acetylacetone, alizarin, aluminon, chloranilic acid, kojic acid, morin, rhodizonic acid, thionalide, thiourea, a-furildioxime, nioxime, salicylaldoxime, dimethylglyoxime, xcex1-furildioxime, cupferron, xcex1-nitroso-xcex2-naphthol, nitroso-R- salt, diphenylthiocarbazone, diphenylcarbazone, eriochrome black T, PAN, SPADNS, glyoxal-bis(2-hydroxyanil), murexide, xcex1-benzoinoxime, mandelic acid, anthranilic acid, ethylenediamine, glycine, triaminotriethylamine, thionalide, triethylenetetramine, ethylenediaminetetraacetic acid (EDTA), metalphthalein, arsonic acids, xcex1,xcex1xe2x80x2-bipyridine, 4-hydroxybenzothiazole, 8-hydroxyquinaldine, 8-hydroxyquinoline, 1,10-phenanthroline, picolinic acid, quinaldic acid, xcex1,xcex1xe2x80x2,xcex1xe2x80x3-terpyridyl, 9-methyl-2,3,7-trihydroxy-6-fluorone, pyrocatechol, salicylic acid, tiron, 4-chloro-1,2-dimercaptobenzene, dithiol, mercaptobenzothiazole, rubeanic acid, oxalic acid, sodium diethyldithiocarbarbamate, and zinc dibenzyldithiocarbamate. However, the most preferred chelating agent is EDTA. In this aspect of the invention, the solution preferably includes an organic solvent as exemplified by alcohol, nitrile, dimethylformamide, tetrahydrofuran, ester, ether, and mixtures thereof. Examples of suitable solvents include methanol, ethanol, 2-propanol, 1-propanol, tetrahydrofuran, ethyl acetate, acetonitrile, and mixtures thereof. The most preferred organic solvent is acetonitrile. In one embodiment, the solution can include a counterion agent such as lower primary, secondary and tertiary amines, and lower trialkyammonium salts, or quaternary ammonium salts. More specifically, the counterion agent can be octylammonium acetate, octadimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, and bromide. However, the most preferred counterion agent is triethylammonium acetate.
In yet a further aspect, the invention provides a method for storing a medium used for separating polynucleotides, e.g., the beads of a MIPC column or a monolith, in order to improve the resolution of double stranded DNA fragments separated using the medium. In the case of a MIPC column, the preferred method includes flowing a solution containing a multivalent cation binding agent through the column prior to storing the column. In a preferred embodiment, the multivalent cation binding agent is a coordination compound, examples of which include water-soluble chelating agents and crown ethers. Specific examples include acetylacetone, alizarin, aluminon, chloranilic acid, kojic acid, morin, rhodizonic acid, thionalide, thiourea, xcex1-furildioxime, nioxime, salicylaldoxime, dimethylglyoxime, xcex1-furildioxime, cupferron, xcex1-nitroso-xcex2-naphthol, nitroso-R-salt, diphenylthiocarbazone, diphenylcarbazone, eriochrome black T, PAN, SPADNS, glyoxal-bis(2-hydroxyanil), murexide, xcex1-benzoinoxime, mandelic acid, anthranilic acid, ethylenediamine, glycine, triaminotriethylamine, thionalide, triethylenetetramine, EDTA, metalphthalein, arsonic acids, xcex1,60 xe2x80x2-bipyridine, 4-hydroxybenzothiazole, 8-hydroxyquinaldine, 8-hydroxyquinoline, 1,10-phenanthroline, picolinic acid, quinaldic acid, xcex1,xcex1xe2x80x2,xcex1xe2x80x3-terpyridyl, 9-methyl -2,3,7-trihydroxy-6-fluorone, pyrocatechol, salicylic acid, tiron, 4-chloro-1,2-dimercaptobenzene, dithiol, mercaptobenzothiazole, rubeanic acid, oxalic acid, sodium diethyldithiocarbarbamate, and zinc dibenzyldithiocarbamate. However, the most preferred chelating agent is EDTA. In this aspect of the invention, the solution preferably includes an organic solvent as exemplified by alcohols, nitriles, dimethylformamide, tetrahydrofuran, esters, and ethers. The most preferred organic solvent is acetonitrile. The solution can also include a counterion agent such as lower primary, secondary and tertiary amines, and lower trialkyammonium salts, or quaternary ammonium salts. More specifically, the counterion agent can be octylammonium acetate, octadimethylammonium acetate, decylammonium acetate, octadecylammonium acetate, pyridiniumammonium acetate, cyclohexylammonium acetate, diethylammonium acetate, propylethylammonium acetate, propyldiethylammonium acetate, butylethylammonium acetate, methylhexylammonium acetate, tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, dimethydiethylammonium acetate, triethylammonium acetate, tripropylammonium acetate, tributylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and mixtures of any one or more of the above. The counterion agent includes an anion, e.g., acetate, carbonate, bicarbonate, phosphate, sulfate, nitrate, propionate, formate, chloride, perchlorate, and bromide. However, the most preferred counterion agent is triethylammonium acetate.